1. Field of the Invention
This invention relates to a power transmission device for a press machine for converting the rotary motion of a crankshaft supported by a frame into a reciprocating motion and transmitting the reciprocating motion to a slide.
2. Description of the Prior Art
In a press machine for converting the rotary motion of a crankshaft into a reciprocating motion and transmitting the reciprocating motion to a slide such as a knuckle press, it is important to keep a bottom dead center position of the slide constant during a working operation. For this reason, in this kind of press machine, it is proposed as a subject to detect the amount of variation of the bottom dead center position and to adjust the bottom dead center position in accordance with the detected amount of variation.
For solving the subject described above, there has been proposed a bottom dead center correcting device for the press machine, in which a movable side supporting point of a knuckle is connected to a slide and a fixed side supporting point thereof is varied by following up the variation of a bottom dead center position (Japanese Patent Public Disclosure (KOKAI) No. 2-165900). In the bottom dead center correcting device, a fixed side supporting point shaft is moved in the vertical direction by supporting a worm wheel eccentrically on the fixed side supporting point shaft of the knuckle and rotating the worm wheel by means of a worm screw meshing with the worm wheel.
In any known bottom dead center adjusting devices, however, the movable side supporting point is connected to a slide. Therefore, when the worm wheel is rotated, the bending and extending range of the knuckle is moved parallel in the vertical direction. Accordingly, the bottom dead center position of the slide can be adjusted, but the stroke length of the slide cannot be adjusted.